Ta có: a + b + c = 0

\(\Rightarrow a^2+b^2+c^2+2ab+2bc+2ac=0\)

\(\Rightarrow2ab+2ac+2bc=-2\)

\(\Rightarrow ab+ac+bc=-1\)

\(\Rightarrow\left(ab+bc+ac\right)^2=1\)

\(\Rightarrow a^2b^2+b^2c^2+a^2c^2+2a^2bc+2ab^2c+2abc^2=1\)

\(\Rightarrow a^2b^2+b^2c^2+c^2a^2+2abc\left(a+b+c\right)=1\)

\(\Rightarrow a^2b^2+b^2c^2+a^2c^2=1\)

Lại có: \(a^2+b^2+c^2=1\)

\(\Rightarrow\left(a^2+b^2+c^2\right)^2=1\)

\(\Rightarrow a^4+b^4+c^4+2a^2b^2+2a^2c^2+2b^2c^2=1\)

\(\Rightarrow a^4+b^4+c^4=1-2\left(a^2b^2+a^2c^2+b^2c^2\right)=-1\)

Ta có: E đối xứng với D qua AB
\(\Rightarrow\) DE là đường trung trực của AB
Vì điểm nằm trên đường trung trực của đoạn thẳng thì cách đều 2 đầu mút \(\Rightarrow\) AE = AD (1)
Lại có: F đối xứng với D qua AC
\(\Rightarrow\) DF là đường trung trực của AC
Vì điềm nằm trên đường trung trực của đoạn thẳng thì cách đều 2 đầu mút \(\Rightarrow\) AF = AD (2)
Từ (1) và (2) \(\Rightarrow\) AE = AF (đpcm).

bạn nói với thầy phynit đi, thầy phynit đổi tên được đó, trên hoc24 này cx có nhiều người được đổi tên rùi, mà đợi thầy đổi tên thì lâu lém (thầy rất bận) nên bn tạo cái nic khác ik, nhanh gọn lẹ

Arrange these words to make complete the sentence:

1. house/ when/ was/ built/ this/ ?
=> When was this house built?

2. made/ how/ cheese/ is/?
=> How is cheese made?

3. computer/ when/ invented/ the/ was/?
=> When was the computer invented?

4. why/ you/ the/ to /party/ come/didn't/ ?
=> Why didn't you come to the party?

5. what/ coming/ your/ time/ friends/are/?
=> What time are your friends coming?

6. concert/ why/ was/ cancelled/the/?
=> Why was the concert cancelled?

Bài 1: change the active into the passive

1. The board awarded the first prize to the reporter

=> The first prize was awarded to the reporter by the board.

2. Have you sent the christmas cards to your family?
=> Have the christmas cards been sent to your family by you?

3. He hides the broken cup in the drawer

=> The broken cup is hidden by him in the drawer.

4. They keep this room tidy all the time

=> His room is kept tidy all the time.

5. They all voted the party a great succes

=> The party was voted a great success.

Viết câu hoàn chỉnh dùng từ cho sẵn

1. I/ going/ write/ letter/ my friend/ tonight
=> I am going to write a letter to my friend tonight.

2. Tom/Mary/ want/ two glasses/ cold water
=> Tom and Mary want two glasses of cold water.

3. Where/ you/ going/ have/ dinner/ tonight
=> Where are you going to have dinner tonight?

4. Uncle/ aunt/ live/ countryside/ now
=> Uncle and aunt are living in countryside now.

5. Nam/ play/soccer/ his friends/ yard/ now
=> Nam is playing soccer with his friends in the yard now.

6. Bill/ going/ take/ computer/ his room
=> Bill is going to take a computer to his room.

7. I/ going/ have/ dinner/ my uncle's house
=> I am going to have dinner at my uncle's house.

8. How often/ you/ watch TV?
=> How often do you watch TV?